Physicians must often commonly access the interior of the human body to perform detailed tissue diagnoses or surgical procedures. As an indispensable tool for such procedures, catheters conveniently provide a means of access without the invasive trauma often associated with, for example, open heart surgery. Inserted within the body's vasculature, such catheters must be precisely controllable to position, as examples, ablation electrodes or imaging probes proximate specific tissues of interest.
To enable precision catheter manipulation within a vasculature, those skilled in the art have implemented control wire mechanisms that selectively "steer" the distal tip of the catheter while the operator inserts the device into the body. Such mechanisms typically include a pair of control wires with distal ends anchored to specific locations at the distal tip of the catheter body corresponding to predetermined deflectional movement. The proximal ends of the wires are mounted to a rotatable actuator that responds to the operator to place one of the wires in tension, pulling at the catheter end for deflection in a first direction, while simultaneously compressing, or buckling, the other wire. An example of such a catheter configuration incorporating such a control mechanism may be found in U.S. Pat. No. 5,383,852, assigned to the assignee of the present invention.
While such devices generally provide a relatively high degree of directional deflection for the catheter tip, over a relatively short period of time the repetitive tensioning and buckling of the control wires may cause control wire fatigue. As a result, the operable lifespan of the device may be substantially shortened.
To address the problem of wire fatigue in a steerable catheter, one proposal, by Thompson (U.S. Pat. No. 5,358,478), discloses a rotatable cam formed with a first cam surface of a first radius on the right side of an asymmetric cam wheel. The left side of the cam wheel is formed with a second cam surface of a second different radius. The rotatable cam includes threaded holes to threadably receive adjustable stops. The proximal ends of the first and second steering cables pass through central openings formed in the respective stops and are attached to respective steering wire terminals.
During operation, by urging the rotatable cam to the left, the second steering wire stop bears against the left terminal block and cam surface. This movement tensions the second steering cable to deflect the catheter tip to the left, while the first steering cable remains relaxed. Likewise, urging of the rotatable cam to the right places the first steering cable in tension while the second steering cable remains relaxed.
While this device works well for its intended purposes, operators may experience fatigue in manipulating the catheter over prolonged periods of time. This may occur because the radius of the cam wheel with respect to the loaded control wire increases as loading increases. The additional loading causes more torque at the actuator, contributing to operator fatigue within a relatively short time.
A second proposal for addressing control wire fatigue, by Lundquist (U.S. Pat. No. 5,395,327), discloses independently tensioning a first steering cable while simultaneously keeping a second steering cable at rest. The device includes two separate cam wheels disposed in-line along the catheter body and attached to respective steering cables. The cam wheels are independently attached to separate operator knobs. During use, the operator rotates one wheel to place one wire in tension and bend the catheter tip accordingly. To effect deflection in another direction, the operator switches to the other knob. As loading increases on each wheel from the tensioning of the respective cables, the torque on the respective knobs correspondingly increases. As a result, operator fatigue can occur within a relatively short period of time. Moreover, because of the dual knob arrangement, operation of the device is somewhat more complex than a unitary knob configuration.
Therefore, there is need for an improved steerable catheter control mechanism which minimizes control wire fatigue. Moreover, a need also exists for a control mechanism capable of minimizing operator fatigue. The control mechanism of the present invention satisfies these needs.